SQL Difference between using = and IN

Question

Whats the difference between using the following statements in a WHERE clause in SQL?

WHERE STUDENTID=7

or

WHERE STUDENTID IN (7)

Is there a recommended/optimal choice?

Answer 1

Use IN if you're doing multiple or's e.g.

Where StudentID = 7 or StudentID = 6 or StudentID = 5

Would be

Where StudentID IN (5,6,7)

Otherwise just use =

Answer 2

There is no functional difference, the result is the same.

Performance would differ if the database treated them differently, but likely the database will recognise that you are using exactly one value in the in expression, and actually make the execution plan as if it was the first one.

You might want to use the first one either way, that makes it clearer that you intended to make an exact comparison, and didn't just forget to put the other values in the in expression.